The present invention generally relates to sensor tracking in a medical procedure. Specifically, the present invention provides a method and system for positioning a tracking sensor for optimal accuracy.
FIG. 1 illustrates an exemplary tracking system 100. System 100 includes an imaging device 110, a table 120, a patient 130, a tracking sensor 140, a medical device or implant 150, tracker electronics 160, an image processor 170, and a display device 180. Imaging device 110 is depicted as a C-arm useful for obtaining x-ray images of an anatomy of patient 130, but may be any imaging device 110 useful in a tracking system. Imaging device or modality 110 is in communication with image processor 170. Image processor 170 is in communication with tracker electronics 160 and display device 180. Tracker electronics 160 is in communication (not shown) with one or more of a tracking sensor attached to imaging modality 110, a tracking sensor attached to medical instrument 150 and sensor 140.
Sensor 140 is placed on patient to be used as a reference frame in a surgical procedure. For example, sensor 140 may be rigidly fixed to patient 130 in an area near an anatomy where patient 130 is to have an implant 150 inserted or an instrument 150 employed in a medical procedure. The instrument or implant 150 may also include a sensor, thereby allowing for the position and/or orientation of the implant or instrument 150 to be tracked relative to the sensor 140. Sensor 140 may include either a transmitting or receiving sensor, or include a transponder.
Typically, in operation, imaging modality 110 obtains one or more images of a patient anatomy in the vicinity of sensor 140. Tracker electronics 160 may track the position and/or orientation of any one or more of imaging modality 110, sensor 140, and instrument 150 relative to each other and communicate such data to image processor 170.
Imaging modality 110 can communicate image signals of a patient's anatomy to the image processor 170. Image processor 170 may then combine one or more images of an anatomy with tracking data determined by tracker electronics 160 to create an image of the patient anatomy with one or more of sensor 140 and instrument 150 represented in the image. For example, the image may show the location of sensor 140 relative to the anatomy or a region of interest in the anatomy.
Sensor 140 and sensors attached or embedded in an implant or medical instrument may be electromagnetic sensors. However, frequently a surgical environment such as system 100 includes several items that may cause interference in the tracking of a sensor relative to another sensor 140. For example, any metal object in the vicinity of the sensors may result in interference to the accurate measurement of one sensor relative to another. Frequently tables 120, imaging devices 110 and other medical instruments 150 contain metal that interfere with such tracking.
Therefore, in order to obtain increased accuracy of tracking an implant or instrument 150 relative to a sensor 140, sensor 140 should be placed as close as possible to a region of interest in a patient 130. For example, as the accuracy of electromagnetic tracking sensors (such as sensor 140) decreases as the distance between sensor 140 and another sensor increases, it is desirable to locate sensor 140 as close to the region of interest as possible.
Current methods and systems include attaching the transmitting sensor 140 to a rigid point of a patient 130. This typically involves fixing sensor 140 onto a bone of the patient 130. A sensor attached to the instrument or implant 150 is then examined to determine if accurate tracking data is obtained from one or more of sensor 140 and the sensor attached to the instrument/implant 150. If inaccurate measurements are obtained (due to interference or otherwise), then sensor 140 must be detached from patient 130 and re-located. For example, in order to rigidly fix sensor 140 to a patient's bone, a surgeon has to cut into the patient. If the sensor 140 is not properly fixed to the bone, the surgeon must detach the sensor 140 from the patient, make another incision into the patient, and re-fix the sensor 140 to the patient. Such a trial-and-error process can result in unnecessary extended periods of time for surgery and unnecessary incisions into a patient anatomy.
Other methods and systems may measure the anticipated accuracy of a sensor 140 fixed to a patient anatomy. Specifically, current methods and systems fix sensor 140 to an anatomy, take several images of the anatomy (while tracking the position of sensor 140 relative to another point, such as the imaging device or while tracking the position of the imaging device relative to sensor 140), and display an estimation of probable tracking inaccuracies. For example, the display may include an image of the patient anatomy with indicators located on the image at various points. The indicators include an estimation of how inaccurate the tracking of sensor 140 may be at that point. For example, one indicator located near the center of the displayed image may indicate that the tracking of a medical device or implant relative to sensor 140 may be inaccurate by up to 2 mm. Another indicator located near the edge of the displayed image may indicate that the tracking of a medical device or implant relative to sensor 140 at that point may be inaccurate by up to 10 mm. In this way, current method and systems may notify a surgeon of the estimated tracking inaccuracies at various points relative to the patient anatomy.
However, these systems and methods do not provide for the positioning of sensor 140 close to a region of interest to increase the accuracy of the tracking system. As described above, these systems and methods merely indicate how inaccurate the tracking of one point relative to a sensor 140 may be at various points. In this way, current systems and methods estimate tracking inaccuracies instead of increasing the accuracy of the tracking system.
Thus, a need exists for a method and system for positioning an electromagnetic tracking transmitter in order to increase the accuracy of a tracking system. Such a method and system can provide for increased accuracy in tracking measurements during a medical procedure by placing a tracking sensor in a position of increased accuracy for electromagnetic tracking measurements. In addition, such a system and method can decrease the time of surgery and amount of invasive procedures into a patient anatomy while increasing the accuracy of a tracking system.